You need to figure out what type of stains they are - this is critical to proper removal. Tannin stains and protein stains need to be handled differently.
I try to use Meguiars D106 and D116 as needed to remove the stains, then either Flex w/citrus or Avenge HD for the pre-extraction pre-spray. In the extractor I use End Zone to properly neutralize any remaining pre-spray.
For cleaning the door panels and hard plastics, it really depends on the level of soil. Steam has replaced a lot of chemicals for me. But generally I use optimum power clean if it's really bad. Otherwise, plain water or the leftover rinseless wash solution.